Colored waste water emitted from a dye house can be changed to colorless, clean water by oxidatively decomposing an organic matter such as dye contained in the waste water. For realization of such a treatment, there has been developed a bubbling method for jetting an oxidative gas, such as ozone, in a state of a bubble into the waste liquid. The bubbled ozone serves as an oxidative gas to decompose and decolorize the dye contained in the waste water. This method makes the waste water clean under the oxidative reaction of the solution, which is caused by a gas-liquid contact. In this method, a tower called a bubble tower is filled with the waste water, and fine bubbles are injected from a bottom portion of the tower. The bubbles go up in the waste water within the bubble tower, and in the course of the bubbles going up to reach the liquid surface, the oxidative gas contained in the bubbles oxidatively decomposes the dye and others to make the waste water clean.
This method, however, presents the following drawbacks.
(1) A finer bubble has to be produced to enlarge a surface area of the bubble, because a speed of reaction is dependent on the surface area of the bubble, i.e., on a diameter of each individual bubble. In order to produce fine bubbles, however, an involved structure does not only become complicated but energy consumption becomes larger accordingly. Further, even when the bubbles are initially fine enough, the bubbles contact one another in the waste water to coalesce, being prone to have an enlarged bubble radius. For such reasons, there exists a problem that a gas-liquid interfacial area decreases which stipulates the speed of reaction.
(2) Further, even if a fine bubble is to be injected, the oxidative gas in the bubble is only able to express an oxidation power to the extent of a gas amount contained in the bubble. That is to say, when the oxidative gas contained in the fine bubble has been exhausted after consumption, the oxidation power is lost even if the bubble goes up while in contact with the waste water. The amount of oxidative gas decreases in accordance with a smaller size of the bubble. For this reason, the smaller the bubble diameter is, the faster the consumption of the oxidative gas is, which means that the oxidation power becomes lost within a shorter time while the bubble goes up in the waste water. As a result, an oxidative gas concentration in the waste water is higher only in the vicinity of the bubble producing unit, making it difficult or impossible for the oxidative gas concentration to be distributed uniformly in the waste water.
(3) Furthermore, when a reaction progresses near a gas-liquid interface, two kinds of transfer phenomena have to be simultaneously proceeded that are a supply of a pre-oxidized substance and a removal of an oxidized product between the oxidative gas in the bubble and the surface of the waste liquid. In order to prompt the reaction, a mixed phase of the waste water and the bubble has to be vehemently agitated so that the two kinds of transfer phenomena may be accelerated. However, there are limits to the speed of transfer for the substance contained in the waste water, which constitutes a factor that the speed of transfer limits the speed of reaction involved in the entire reactor.
As a reaction method to remedy such drawbacks, there has been developed a method of spraying a solution into an ozone gas. Refer to the Patent Documents 1 and 2.                Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-326285        Patent Document 2: Japanese Patent Laid-Open Publication No. H09-239383 (1997)        